The proposed research has four broad aims. First, using a natural experiment, termed school cut-off, the work seeks to examine in depth the nature, timing, and magnitude of cognitive changes in children from kindergarten through elementary school. Second the research will endeavor to trace the influences of experiences in school (and during the summer) that parallel (and might mediate) changes in cognitive skills over the age period studied. Third, the research will explore in greater depth and over a longer age range the feasibility and sensitivity of the school cut-off method for understanding the nature and sources of cognitive growth. Fourth, the research will extend the applicability of Hierarchical Linear Models to new designs and methods. Two groups of children (old kindergarten and young first grade) who just miss versus just make athe cut-off for first grade, will be selected. The groups will be closely matched on chronological age and other relevant background variables. Children will receive a battery of literacy skills taste (reading, math, language, memory, and general knowledge) at the beginning and end of each year. Comparisons of the degree of progress made by old kindergarten and young first grade children, will reveal the extent to which changes in literacy skills were produced by schooling-related or age-related influences. Similar comparison during the summer period will examine group differences in family-related experiences. Concurrently, detailed information will be gathered on classroom activities and characteristics in an attempt to examine more directly the relation between instructional activities and growth of literacy skills. As an outgrowth of the framework developed here, a number of novel developmental phenomena may be elaborated including indirect effects, dissociation effects, and delayed transfer effects. Results from the proposed study will yield a more complete and comprehensive picture of cognitive growth in early school-age children. Findings will illuminate the complex, intricate ways that developmental change may proceed in the same child. Further, the study will help to illustrate the feasibility of conducting solid, empirical research within the framework of a complex, multi-level, interfactional model of development. Finally, the research has implications for educational policy and practice. Findings will address a recent controversy regarding whether children who are relatively young at school entry are at risk for academic problems. In addition, results will yield valuable information on the kinds of literacy skills children are acquiring in school and whether important literacy skills are being neglect ed in the curriculum.